1. Field of the Invention
The present invention relates to a compressor and, more precisely, it relates to a compressor in which the tilt angle of a cam plate is varied by a hinge mechanism to thereby vary the stroke of a piston.
2. Description of the Related Art
In a variable displacement compressor used in an air conditioner circuit for automobiles, a crank chamber is formed in a housing and a drive shaft which is rotatably supported in the crank chamber is driven by an engine to suck or discharge a refrigerant. In general, in this type of compressor, a cylinder block which constitutes a part of the housing is provided with a cylinder bore in which a piston is reciprocally moved. A lug plate, as a rotary support, is secured to the drive shaft so as to rotate with the shaft. A swash plate is operatively connected to the lug plate. The operative connection between the lug plate and the swash plate is such that the swash plate is rotatable together with the lug plate and can vary the angle defined between the swash plate and the drive shaft through a hinge mechanism. The piston is operatively connected to the outer peripheral portion of the swash plate, so that when the drive shaft is rotated, the reciprocal movement of the piston takes place to suck or discharge the refrigerant. Moreover, the angle of the swash plate with respect to the drive shaft can be varied by controlling the pressure in the crank chamber in order to vary the stroke of the piston.
In the conventional compressor mentioned above, since radial and thrust loads are exerted on the drive shaft, through the swash plate or the lug plate, it is necessary to provide bearings to receive the loads in the radial and axial directions. Moreover, due to a difference in pressure between the inside and the outside of the housing, it is necessary to provide a seal member in a gap between the housing and the drive shaft. Furthermore, it is necessary to provide a coil spring to continuously bias the swash plate in a direction to reduce the stroke of the piston. The coil spring is, in general, wound around the drive shaft between the swash plate and the lug plate.
The space for accommodating the bearings, the seal member, and the coil spring increases the overall length of the compressor and reduces the freedom of the arrangement thereof in a narrow engine compartment.
To eliminate these drawbacks, in a compressor disclosed in Japanese Kokai (Unexamined Patent Publication) No. 8-312529, the radial bearing which receives the load in the radial directions is provided between the lug plate secured to the drive shaft and the housing. The lug plate is provided, along the periphery of the drive shaft, with a recess in which the seal member is received, so that the seal member overlaps the bearing in the axial direction of the drive shaft.
In a compressor disclosed in Japanese Kokai No. 9-60587, the coil spring is received in the recess formed in the lug plate along the circumferential direction of the drive shaft, so that the coil spring can be moved to the front of the compressor.
However, in the compressor disclosed in Japanese Kokai No. 8-312529, the improvement is addressed only to the arrangement of the bearing and the seal member, and there is no specific reference in JPP ""529 to a solution to the drawback of an increase in the overall length of the compressor due to the presence of the coil spring. In the compressor disclosed in Japanese Kokai No. 9-60587, the coil spring, the bearing, and the seal member are arranged on the drive shaft in line along the axis of the drive shaft. In this arrangement, if the depth of the recess in which the coil spring is received is increased in the forward direction of the compressor, the strength of the securing portion of the lug plate and the drive shaft tends to be insufficient and no reduction of the overall length of the compressor is considered in JPP ""587.
It is an object of the present invention to provide a compressor in which not only can the overall length thereof be reduced (miniaturized) without reducing the strength of the rotary support but also the rigid connection between the rotary support and the drive shaft can be ensured.
To achieve the object mentioned above, according to the present invention, there is provided a compressor in which a drive shaft is rotatably supported in a housing which defines therein a crank chamber; a cylinder block which forms a part of the housing is provided with a cylinder bore; a piston is received in the cylinder bore so as to reciprocally move; a rotary support is secured to the drive shaft so as to rotate together therewith; a cam plate is operatively connected to the rotary support through a hinge mechanism which connects the cam plate to the rotary support so as to rotate together therewith and to vary an angle with respect to the drive shaft; said piston is operatively connected to the cam plate so that the rotation of the drive shaft causes the piston to reciprocally move to thereby suck and discharge a refrigerant and that the stroke of the piston can be varied by varying the angle of the cam plate with respect to the drive shaft, wherein a radial bearing is provided between the outer peripheral surface of a boss portion formed on the rotary support and the housing to support the drive shaft, and a coil spring is wound around the drive shaft between the cam plate and the rotary support to bias the cam plate in a direction to reduce the stroke of the piston, said coil spring being inserted in a spring receiving portion formed in the rotary support on the side thereof opposite the boss portion, the diameter of the outer periphery of the boss portion being greater than the diameter of the spring receiving portion.
With this structure, even if the radial bearing and the coil spring are located in close proximity in the axial direction of the drive shaft, since the radial bearing is provided on the outer periphery of the boss portion whose diameter is greater than the diameter of the spring receiving portion, a contact surface area necessary to fit and engage the rotary support to and with the drive shaft can be easily provided therebetween. Namely, it is easy to maintain the necessary strength for the fitting and engagement of the rotary support and the drive shaft. Moreover, it is possible to prevent the spring receiving portion from being too close to the outer periphery of the boss portion on which the radial bearing is provided, and hence the sufficient strength of the rotary support itself can be easily obtained. Consequently, the miniaturization of the compressor in the axial direction of the drive shaft (reduction of the overall length of the compressor) can be facilitated.